Substrate confinement apparatus and method

ABSTRACT

A method and apparatus for constraining a substrate in-plane is provided. A substrate retainer having a retainer body and contact surface configured to engage a portion of a back side of a substrate, and a flexure coupled to the retainer body and configured to restrict one or more degrees of movement of a substrate with respect to the substrate retainer.

FIELD OF THE INVENTION

Disclosed embodiments of the invention relate to the field of substrateprocessing, and more particularly, embodiments of the invention relateto constraining a substrate in specified coordinates during processing,such as for substrate chucking at lithography.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings, in which thelike references indicate similar elements and in which:

FIG. 1 illustrates a cross-sectional view of a substrate confinementapparatus in accordance with an embodiment of the present invention;

FIG. 2 illustrates top view of a substrate confinement apparatus andsubstrate in accordance with an embodiment of the present invention;

FIG. 3. Illustrates a cross-sectional view of a substrate confinementapparatus in accordance with an embodiment of the present invention; and

FIG. 4 illustrates a process for confining and unconfining a substratein accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration specific embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present invention. Therefore, the following detaileddescription is not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

Embodiments in accordance with the present invention provide a substrateconfinement apparatus and a substrate confinement method that may assistin the confinement of a substrate, such as a silicone wafer, in fixedcoordinates with respect to a confinement apparatus, despite the forcesthat are imposed on a substrate as it is being processed or transferredfrom one process to another. One or more substrate retainers inaccordance with the present invention may be used to improve control ofthe top surface, such as planarity, despite local imperfections on asubstrate back side or on the substrate chuck.

Current substrate confinement apparatuses are often referred to as“wafer chucks”, which typically may confine a substrate in differentways. One such example is known as a contactless chuck, where aplurality of air jets and vacuum ports may be used to maintain thesubstrate in a substantially planar position and achieve lateral (X, Yand potentially Θ) in plane confinement through mechanical contact andthe substrate side. Another wafer chuck is a low contact area chuck,which confines a substrate with direct contact of a large vacuumoperated seal positioned about the outer periphery of the substrate withseveral inner hard supports positioned within the perimeter of the sealfor supporting the interior portion of the substrate. Other higher areacontact chucks may also be used.

Contactless chucks allow more in-plane movement that is desired, asthere may be some tolerance between the mechanical contact with thesubstrate sides. Contact chucks, on the other hand, constrain thesubstrate on a very small lateral spatial scale, such that the substratecannot properly relax into a chucked position conformal with the surfaceof hard contact. Additionally, contact surface particulate contaminationand wear can cause out of plane confinement and impact processing sideplanarity. In one embodiment in accordance with the present invention awafer may be constrained in-plane, such that lateral movement in eitherthe X, Y or rotational Θ is restricted with minimal substrate contact,allows the substrate to properly relax into a chucked position. Andthough some contact is made, it can accommodate certain wear and/orcontamination issues and maintain global planarity of the process sideof the substrate.

FIG. 1 illustrates a cross-sectional view of a substrate confinementapparatus in accordance with an embodiment of the present invention. ASubstrate 10, which may be for example a silicon wafer, is in a positionfor processing of the process side 12 of substrate 10. As shown, thewafer may be fully confined and also said to be in the “chucked state.”Examples of processing stages where the substrate may need to be in thechucked state include, but are not limited to, lithography, chemicalmechanical polishing (CMP), inspection and metrology andtransfer/transport. Accordingly, in these and other processes it may benecessary that process side 12 of substrate 10 to remain globally planarand in fixed coordinates so it does not move in certain directions, butmay allow for local independent movement of portions of the back side,depending on situations such as back side imperfections, particulatecontamination, chuck irregularities and the like.

As shown, substrate 10 may be constrained in-plane and restrained in oneor more degrees of lateral movement. Substrate 10 may be so confined byat least one or more substrate retainers 20 in accordance withembodiments of the present invention. Thus, when movement within a planeis to be restricted (e.g. lateral movement) three degrees of substratemovement that may be resisted by the substrate retainer 20 includesmovement along the X and Y axes and movement in the rotational Θdirection, shown by the coordinate legend 8.

Substrate retainer 20 may include a retainer body 22 and flexure 30, andwhen coupled to the substrate back side 14, may allow for local out ofplane substrate movement in the vertical Z direction, while confining inplane lateral movement. Absence of hard local confinement in the Zdirection may be necessary during certain processes, such aslithography, to enable the substrate being processed to appropriatelyrelax into a globally planar confined state. In cases, such as CMP, suchZ movement may be needed for uniform back side pressure, or locallyspatially modulated back side pressure as may be required for CMPmaterial removal of a process side so it can be processed into a planarsurface.

Substrate 10 may be substantially confined to a single plane through theuse of a global confinement system such as a pressure control systemusing alternating vacuum ports 16 and air jets 18 or an electrostaticcontrol system, or some other known form of confinement. The vacuumports 16 and air jets 18 work in conjunction with one another providingsufficient upflow and downflow, such that the substrate 10 may be heldin-plane without having significant out of plane warp or movement ofsubstrate 10 in the Z direction to maintain control of the process side12 of substrate 10.

The alternating vacuum ports 16 and air jets 18 alone, however, do notrestrict movement in the X, Y or Θ directions. In typical contactlesschucks, some form of mechanical interface is required with the edges ofthe substrate to restrain X and Y and Θ movement. However, themechanical interface allows for some movement, as some tolerance mustexist between the substrate edge and the mechanical interface,otherwise, the substrate cannot float and move, if necessary, in the Zdirection.

In an embodiment in accordance with the present invention, retainer 20may be used to restrain in-plane movement of substrate 10 and maintainthe X, Y and Θ coordinates, as well as allow for local independentmovement in the Z direction. Retainer 20 may include a retainer body 22that has a contact surface 24 configured to removably couple withsubstrate back side 14. Retainer body 22 and contact surface 24 mayremovably couple to substrate back side 14 through the use of a vacuumand/or suction effect. A number of other techniques may be used tointerconnect retainer body 22 and contact surface 24 to the substrateback side 14, including, but not limited to, electrostatic forces,VanderWaals force, magnetic forces, and meniscus and capillary forceswhere an interface material may be used.

Retainer body 22 may be coupled to a flexure 30. Flexure 30 may be astiff membrane, and may be designed to allow unhampered motion in one ormore directions, but is extremely inflexible in other directions. Thus,for example, where movement is only desired in the Z direction, as shownby position 32 for example, flexure 30 may be designed to restrictlateral movement in the X and/or Y directions, as well as restrictrotational movement in the Θ direction. Flexure 30 may then allowfreedom of movement in the Z direction, as shown by flexure position 32.

The coupling of the retainer body 22 to the flexure 30 may be through avariety of ways, including, but not limited to, a mechanicalinterconnection, such as a rivet, screw, or welding, and/or achemical/mechanical interconnection, such as an adhesive. In an otherembodiment, the retainer body and the flexure may be made out the samematerial as a unit.

Under ideal conditions, there would likely be little or no need for thesubstrate 10 to move in the Z direction. However, due to a variety ofreasons, including, but not limited to, substrate back sideimperfections, processing irregularities and the presence ofcontaminants, portions of the substrate back side 14 may need to beallowed out of plane on back side 14, which may require locally allowinglimited Z movement, to improve planarity of the process side 12, andglobally confining the overall Z movement of the front side, whileconstraining the in-plane degrees of freedom.

Substrate retainer 20 achieves such a result, in that it may allow localZ movement as required for global planarity of the process side 12 andrestrain movement out of the X, Y or Θ coordinates, which may becoordinates that need to be maintained throughout the process. It can beappreciated however, that other coordinates may also be constrained, asneeded, including the Z coordinate, such that the flexure allowsmovement in another direction, depending on the process and substratebeing processed. This may be accomplished by selecting a flexure andmaterial that meets such movement controlling parameters.

Suitable materials for flexure 30 may include metal-based materials,such as steel, aluminum, and other alloys, as well as non-metal-basedmaterials, such as glass, quartz, synthetic diamond, sapphire, and thelike. The flexure may also be configured or supported in several ways,including, but not limited to single sheet having two points ofattachment.

As illustrated in FIG. 1, two substrate retainers 20 may be coupled tothe substrate back side 14. In such a case, each retainer body 22 may becoupled to a corresponding flexure 30 and 30′ respectively, which may beconfigured to restrain lateral movement. Either substrate retainer mayconstrain X movement and the other constrain Y movement. The substrateretainers 20 may be positioned at different points away from the centerof the substrate 10, and together may operate to constrain rotationalmovement or the Θ coordinate. The two substrate retainers may beconfigured to independently allow movement in the Z direction such thatthe substrate may properly settle into a chucked state and control theplanarity of the process side 14, while allowing for back sideirregularities, such as substrate back side 12 imperfections.

FIG. 2 illustrates a top view of a substrate and substrate confinementapparatus in accordance with an embodiment of the present invention.Three substrate retainers may be horizontally spaced apart from eachother in a generally equilateral relation fashion. Similar to a tripod,this configuration may provide sufficient support at enough points onthe substrate back side to provide a substantially uniform support ofthe substrate 10 for it to be lowered into the plane of confinement orlifted from the plane of confinement. The three substrate retainers 20may also provide substantial lateral confinement, restricting severaldegrees of freedom, including X, Y and Θ. As with the embodiment wheretwo substrate retainers are used, each substrate retainer may allow forlocal Z movement, but overall global confinement may be sufficientlyconstrained by the global confinement system, such as alternating airjets and vacuum ports.

In other embodiments, more than three substrate retainers may be used toallow certain degrees of freedom and restrict others. The more contactpoints made with the substrate back side, however, may create additionalproblems that are undesirable in certain applications, including, butnot limited to the problem of the substrate to not properly relax into afully constrained position as is the case in the currently used contactand low contact area chucks. In other cases, having redundant substrateretainers can be a benefit, such as when a back side surface does notuniformly enable effective attachment, or where independent operation ofback side retainers may be used to assure failure free operation, evenwhere one retainer fails to attach due to particulate surfacecontamination. Redundant arrays of substrate retainers may also avoidatomic or ionic cross contamination of processes, such that—where onesubs-set of substrate retainers have contacted a copper bearingsubstrate, for example, if a non-copper bearing substrate were to be runin the same machine, the other redundant sub-set of substrate retainersmay be used to avoid cross contamination and maximize machine usage.

In another embodiment, if positioned in the center of the substrate, asingle substrate retainer 20 may be used to restrict at least one ormore degrees of movement. However, given the potential forcesencountered by the substrate that may be translated to the substrateretainer, and the potential size difference between the substrate beingprocessed and the retainer contact surface 24, multiple retainer bodiesmay better restrict certain degrees of movement.

Whether using a single or multiple substrate retainers, the substrateretainers may be carried by a stage that coordinates the movement of thesubstrate retainers with other elements of a substrate chuck.

A problem that may arise, particularly when processing ultra-thinsubstrates, is potential for dimpling. Dimpling may be inward toward theretainer body, such as may result when a suction/vacuum connection ismade, or outward creating a bump in the process side where otherattractive forces are used. Dimpling may be caused by the interfacebetween the contact surface and the substrate back side in conjunctionwith the forces being exerted.

Accordingly, referring to FIG. 1, when vacuum is used, for example, tosecure the substrate retainer 20 to the substrate back side 14, using asmaller diameter contact surface 24 and reducing the inner diameter ofthe aperture 26 may help resist the inward dimpling effect, which inturn may cause the process side 12 of substrate 10 to be more unaffectedby any back side interconnection. In the alternative, or in addition to,the number of substrate retainers may be increased to gain in-planefriction with out dimpling over individual substrate retainers. Thoughnot required, it has been found that a diameter for aperture 26 may beapproximately 2 mm without resulting in significant dimpling onsubstrates that are on the order of approximately 0.5 mm in thickness.It can be appreciated, however, that the thinner the substrate, theinner diameter may be reduced to avoid dimpling effects.

Likewise, if a different method to removably couple the retainer body tothe substrate back side 14 is used, such as electrostatic force, acontact surface diameter that is too small may increase the outwarddimpling effect. It may therefore be necessary, depending on thecoupling method used, to adjust the contact diameter of the retainerbody to resist dimpling by either decreasing or increasing the diameterof the retainer bodies as necessary.

Another problem that may occur is the eventual wear of the contactsurface, due to its contact with a substrate back side. Wear on thecontact surface may hamper the ability of retainer to securely couple tothe substrate back side. Uneven wear among multiple retainer contactsurfaces may cause the substrate to not be properly confined toparticular coordinates. Although contact surface wear, even non-uniformwear, may be tolerated by substrate retainer embodiments in accordancewith the present invention, as the flexure movement may compensate forsurface wear, to help avoid such wear, for example, a hard surfacingmaterial may be applied to the contact surface, or, the retainer body bemade of a solid hard material. Such hard facing materials may include,but are not limited to, diamond facing or carbide coating. Additionally,redundant substrate retainers may be included in the substrate chucksuch that depending on the process, fewer or more than three retainersmay be used. Or, if a substrate retainer contact surface is worn, aredundant substrate retainer may be used while the worn retainer isreplaced.

FIG. 3 illustrates a cross-section of a substrate confinement apparatusin accordance with an embodiment of the present invention. As shown, anactuator 40 may be used to facilitate the chucking or dechucking of asubstrate 10. Actuator 40 may raise to support the flexure 30 andretainer body 22 in an up/receiving position when substrate 10 isbrought into position for processing. The support provided by actuator40 may allow retainer body 22 to couple or decouple to the substrateback side 14.

Actuator 40 can supply the necessary coupling medium to the retainerbody to enable coupling to the substrate back side, such as a vacuum orelectrostatic force. For example, actuator 40 can act to provide thenecessary vacuum to retainer body 22 to enable coupling to the substrateback side 14, if vacuum and suction is the method of coupling. Actuator40 may also relieve the pressure to break the vacuum is decoupling isdesired. Once coupled or decoupled, the actuator 40 may then retract (asseen in FIG. 1) to allow the substrate to settle into the positiondictated by the global Z confinement, such as the alternating air jets18 and vacuum ports 16.

Embodiments in accordance with the present invention may be suitable forapplication in lithography and may be used in conjunction withcontactless chucks to enable lateral in-plane confinement, as well asenable a higher degree of substrate conformance to the surface of thecontactless chuck. Embodiments in accordance with the present inventionmay also be suitable for substrate confinement in Chemical MechanicalPolish (CMP) processes to enable better control of substrate back sidepressure and accommodate substrate back side surface imperfections.

Embodiments in accordance with the present invention may also besuitable for substrate confinement where translation in one or more axisor degrees of freedom may be allowed or required, such as in precisionpositioning devices like Flexure Stages. Embodiments in accordance withthe present invention may also be suitable for substrate confinement incontactless transfer arms and end-effectors. Embodiments in accordancewith the present invention may also be suitable for substrateconfinement for back side contactless substrate transport devices wherea substrate is riding from one point in space to another and isconstrained in plane so as to not come into hard contact with the wallsof the substrate transporter.

Substrate confinement in lithography may tend to attain a desired globalplanarity, with the tightest restriction on substrate movement. Whereas,in CMP, some degree of substrate movement may be tolerable, and intransport/transfer operations may be even more so. Excessive lateralmovement, however, in general is undesirable in many processes.

Another embodiment of the present invention may include a flexible backside constraint for substrates in a substrate carrier that may havelimited back side only contact, which may allow for considerableflexibility and independent travel to absorb the forces encountered, butmaintains the substrate in a confined state and precludes hard contactwith the stage or carrier of the substrate and substrate retainers.

FIG. 4 illustrates a process for chucking and dechucking a substrate inaccordance with an embodiment of the present invention. A substrateconfinement apparatus is provided having at least one substrate retainerin accordance with an embodiment of the present invention (100). ASubstrate may be positioned in the substrate confinement apparatus forprocessing (110). This can be done in a number of ways, including butnot limited to an end-effector bringing the substrate to the confinementapparatus. An actuator may be used to urge the flexure and retainer bodytoward the substrate, and thereby urge a contact surface of the retainerbody into contact with the substrate back side (120). The retainer bodymay be coupled to the substrate back side (130). This coupling may bethrough number of coupling forces, such as vacuum/suction applied thoughthe actuator. The actuator may be retracted from the flexure andretainer, thereby leaving the retainer coupled to the substrate backside and allow substrate and substrate retainer to settle into a neutralstate (140). The global confinement system may be activated to maintainthe substrate in a substantially planar position (150). In oneembodiment the global confinement system may include a plurality ofalternating air jets and vacuum ports. Once confined in plane andrestricted from lateral in plane movement, the substrate is ready forprocessing. To de-chuck the wafer, a reverse of the above process may beused.

Although specific embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent implementations calculated to achieve thesame purposes may be substituted for the specific embodiment shown anddescribed without departing from the scope of the present invention.Those with skill in the art will readily appreciate that the presentinvention may be implemented in a very wide variety of embodiments. Thisapplication is intended to cover any adaptations or variations of theembodiments discussed herein. Therefore, it is manifestly intended thatthis invention be limited only by the claims and the equivalentsthereof.

1. A substrate retainer, comprising: a plurality of retainer bodies,configured to removably engage a substrate having a back side, whereineach retainer body engages a corresponding inner portion of the backside and the plurality of retainer bodies collectively engage less thanthe entire back side; and a flexure coupled to one of the retainerbodies, configured to restrict one or more degrees of movement of thesubstrate with respect to the substrate retainer.
 2. The substrateretainer of claim 1, wherein one of the retainer bodies removablyengages the back side of the substrate through vacuum control.
 3. Thesubstrate retainer of claim 2, wherein one of the retainer bodiesincludes a contact surface, and an aperture extending through a portionof the contact surface to allow activation and deactivation of a vacuum.4. The substrate retainer of claim 1, wherein the retainer bodyremovably engages the portion of the back side of the substrate througha coupling method selected from electrostatic force, VanderWaals force,magnetic forces and capillary attraction.
 5. The substrate retainer ofclaim 1, wherein one of the retainer bodies includes a contact surfaceto mate with the back side of the substrate, and the contact surface isfaced with a wear-resistant material.
 6. The substrate retainer of claim1, wherein the flexure is configured to resist in-plane lateralmovement, and allows out-of-plane movement.
 7. The substrate retainer ofclaim 6 wherein the in-plane lateral movement restricted by the flexureis movement in at least a selected one of a X, a Y and a θ direction,and the out-of-plane movement allowed by the flexure includes a Zdirection.
 8. The substrate retainer of claim 1, wherein the flexurematerial is a selected one of steel, aluminum, glass, quartz, syntheticdiamond, and sapphire.
 9. The substrate retainer of claim 1, furthercomprising an actuator configured to controllably urge the flexure andthe retainer body in an upward direction to facilitate chucking anddechucking of the substrate.
 10. The substrate retainer of claim 9,wherein the actuator controls the coupling of the retainer body to theback side of the substrate.
 11. A substrate confinement apparatus,comprising: a global confinement system that causes a substrate tosubstantially remain in one plane; and one or more substrate retainers,at least one of which including: a plurality of retainer bodies,configured to removably engage a a substrate having a back side, whereineach retainer body engages a corresponding inner portion of the backside and the plurality of retainer bodies collectively engage less thanthe entire back side; and a flexure coupled to one of the retainerbodies and configured to restrict one or more degrees of movement of thesubstrate with respect to the substrate retainer.
 12. The substrateconfinement apparatus of claim 11, wherein three or more substrateretainers are used and equilaterally spaced from each other.
 13. Thesubstrate confinement apparatus of claim 11, wherein one of the retainerbodies removably engages the back side of the substrate through vacuumcontrol.
 14. The substrate confinement apparatus of claim 11, whereinone of the retainer bodies includes a contact surface, and an apertureextending through a portion of the contact surface to allow activationand deactivation of a vacuum.
 15. The substrate confinement apparatus ofclaim 11, wherein the retainer body removably engages the portion of theback side of substrate through a coupling method selected fromelectrostatic force, VanderWaals force, magnetic forces and capillaryattraction.
 16. The substrate confinement apparatus of claim 11, whereinone of the retainer bodies includes a contact surface to engage the backside of the substrate, and the contact surface is faced with awear-resistant material.
 17. The substrate confinement apparatus ofclaim 11, wherein the flexure is configured to resist in-plane lateralmovement, and out-of-plane movement.
 18. The substrate confinementapparatus of claim 17 wherein the in-plane lateral movement restrictedby the flexure is movement in at least a selected one of a X, a Y and aθ direction, and the out-of-plane movement allowed by the flexure is a Zdirection.
 19. The substrate confinement apparatus of claim 17, whereinthe global confinement apparatus maintains the substrate generally inone plane and the one of the substrate retainers allows for independentlocal out-of-plane movement of the substrate.
 20. The substrateconfinement apparatus of claim 11, wherein the flexure material is aselected one of steel, aluminum, glass, quartz, synthetic diamond, andsapphire.
 21. The substrate confinement apparatus of claim 11, furthercomprising an actuator configured to controllably urge one of thesubstrate retainers in an upward direction to facilitate loading andunloading of the substrate.
 22. The substrate confinement apparatus ofclaim 11, wherein the global confinement system includes a plurality ofvacuum ports and air jets, and a pressure control to maintain thesubstrate in substantially one plane.
 23. A substrate confinementmethod, comprising: providing a substrate having process side and a backside; providing a substrate confinement apparatus having one or moresubstrate retainers, at least one of the substrate retainers including aplurality of retainer bodies configured to removably engage a substratehaving a back side, wherein each retainer body engages a correspondinginner portion of the back side and the plurality of retainer bodiescollectively engage less than the entire back side, and a flexurecoupled to one of the retainer bodies and configured to restrict one ormore degrees of movement of the substrate with respect to the substrateretainer; positioning the substrate in the substrate confinementapparatus; urging one of the substrate retainers toward the back side ofthe substrate; and coupling a contact surface of one of the retainerbodies to the back side of the substrate; and activating a globalconfinement system.
 24. The substrate confinement method of claim 23,further comprising: processing the substrate; and decoupling thesubstrate retainer from of the back side of the substrate.
 25. Thesubstrate confinement method of claim 23, wherein urging one of thesubstrate retainers toward the back side of the substrate includesproviding an actuator and raising the actuator to engage the flexure.26. The substrate confinement method of claim 23, wherein coupling thecontact surface of one of the retainer bodies to the back side of thesubstrate includes supplying a vacuum to the retainer body.
 27. Thesubstrate confinement method of claim 25, further comprising: removingthe actuator from the flexure.